Differential observables for software-based GPS interferometry

The implementation of an interferometric positioning experiment for measuring the baseline vector between two locations is presented. Two identical software receivers, each consisting of an antenna, a low-cost USB front-end collecting GNSS signals in the L1 band and a laptop, are placed at both ends of the baseline. Cross-correlating the raw signals in post-processing yields differential code delay and carrier frequency observables. A three dimensional baseline vector can be computed after applying corrections to the ranging measurements. Issues related to producing differenced observables, such as the correlation of two noisy signals, the detection and identification of all satellites and issues arising from hardware features of the receivers such as the synchronisation of the two receivers are addressed.